1. Field of the Invention
The present invention relates to fire-resistant structural composite materials. Embodiments of the present invention pertain to formulations of commercially available components that form a composite material having superior structural, fire, smoke and toxicity characteristics. More particularly, embodiments of the present invention relate to composite formulations and structures including a phenolic-based resin system, fiber, and alumina tri-hydrate.
2. Description of Related Art
Structural composites have found use in applications where light weight, high strength and economy are important, such as, for instance, in the automotive, aircraft and ship building industry. A wide variety of structural composite materials have been developed for these applications. In some applications in which flame resistance and/or fire protection requirements are imposed, fire-resistant composites are necessary. However, fire-resistant composites are more challenging to develop and produce, especially in an economical manner, and are often unsatisfactory in structural applications when used without an underlying support structure.
The United States Department of Defense has established a test method standard and acceptance criteria for fire-resistant composite materials to be used in Naval submarines—MIL-STD-2031 (Department of Defense Test Method Standard: Fire and Toxicity Test Methods and Qualification Procedure for Composite Material Systems Used in Hull, Machinery, and Structural Applications inside Naval Submarines (26 Feb. 1991)). The standard establishes fire and toxicity test methods, requirements and the qualification procedure for composite material systems. These standards have been established to ensure that composite materials designed for such purposes are not a primary fire source, are slow to ignite and can be extinguished using normal submarine fire fighting response, and that the toxicity effects can be tolerated, particularly in the closed environment of a submarine. Engineers have found it extremely difficult to design composites that pass these standards.
One of the conventional methods of forming fire-resistant composites that meet the requirements of MIL-STD-2031 is the inclusion of fire insulation or foam, which works by providing an air space between the fire and the remaining composite structure. However, one of the disadvantages of using these composites is that the insulation or foam significantly increases the volume of the composite panel. Another conventional method of forming fire safe composites is by using metallic structures. This eliminates the need to resolve fire safety specification requirements as this is the existing accepted material, however it increases the weight and decreases corrosion-resistance properties of the composite panel.
Other methods of forming fire-resistant composites have been attempted to overcome the disadvantages of the above-mentioned methods, however these composites are unable to pass the acceptance criteria of MIL-STD-2031. One such method is coating a structural composite with a substance that imparts fire resistance. However, disadvantages to this method include additional processing steps associated with the coating process, and the break-down of the coating over time, which diminishes the fire-resistance properties of the panel. Another such method is forming the composite panel from a resin or fiber-reinforced resin. Although some resins are known for their fire-resistant properties, these resin-based composites have proven unsuitable because their exposure to heat and flames typically results in the release of by-products including chemical compounds and gases that are flammable, toxic to the environment, and pose a safety hazard if inhaled.